1. Field of the Invention
The present invention relates to a picture display apparatus for projecting an image onto a screen and so on through spatially modulating light emitted from a light source. The invention further relates to a cooling apparatus used for an optical apparatus having a light source and an optical system through which light emitted from the light source passes, the cooling apparatus being provided for cooling a section including at least part of the optical system.
2. Description of the Related Art
Liquid crystal projectors have been developed as picture display apparatuses intended for showing a picture, for example. Such a liquid crystal projector spatially modulates light from a light source radiating at a liquid crystal light valve and projects light transmitted through the liquid crystal light valve onto a screen and so on through a projection lens so as to display an image.
A related-art liquid crystal projector will now be described, referring to drawings. FIG. 1 to FIG. 4 show the related-art liquid crystal projector. FIG. 1 is a perspective view showing the main part of the projector. FIG. 2 is a top view showing the main part of the projector. FIG. 3 is a cross section illustrating a configuration of the projector including a liquid crystal light valve, a polarizing plate and a cooling fan. FIG. 4 is a perspective bottom view showing the main part of an optical unit of the projector.
The liquid crystal projector 100 comprises: an enclosure not shown; a board 101 provided in the enclosure; a light source 102 provided on the board 101; and an optical unit 103 for spatially modulating light emitted from the light source 102 and projecting the modulated light onto a screen and so on not shown. The top of the optical unit 103 is mostly covered with a lid 121 while part of the top of the optical unit 103 is uncovered. On top of the lid 121, a drive circuit board 104 is provided. The drive circuit board 104 includes a drive circuit for driving liquid crystal valves described later.
The optical unit 103 includes: a cubic composite prism 105; a liquid crystal light valve 106R opposed to a surface 105R of the prism 105; a liquid crystal light valve 106G opposed to another surface 105 G of the prism 105 orthogonal to the surface 105R; a liquid crystal light valve 106B opposed to another surface 105B of the prism 105 parallel to the surface 105R; and a projection lens 116 placed on a side of another surface of the prism 105 parallel to the surface 105G. Polarizing plates 112R, 112G and 112B are each provided on a side of each of the light valves 106R, 106G and 106B that is opposite to a side facing the prism 105. Furthermore, condenser lenses 113R, 113G and 113B are each provided on a side of each of the polarizing plates 112R, 112G and 112B that is opposite to a side facing each of the light valves 106R, 106G and 106B.
In the projector 100, white light emitted from the light source 102 and entering the optical unit 103 goes through a ultraviolet-infrared (UV-IR) cut filter 107, a fly's-eye lens 109 made up of a lens array 109a and 109b and through a main condenser lens 108 and enters a dichroic mirror 111a. Red light of the light entering the dichroic mirror 111a reflects off the dichroic mirror 111a and further reflects off a reflection mirror 114a. The red light then passes through the condenser lens 113R and the polarizing plate 112R. The red light is then spatially modulated by the light valve 106R based on an image signal for a red image and enters the prism 105. The light entering the dichroic mirror 111a other than the red light is transmitted through the dichroic mirror 111a and enters the dichroic mirror 111b. Green light of the light entering the dichroic mirror lib reflects off the dichroic mirror 111b and passes through the condenser lens 113G and the polarizing plate 112G. The green light is then spatially modulated by the light valve 106G based on an image signal for a green image and enters the prism 105. Blue light of the light entering the dichroic mirror 111b is transmitted through the dichroic mirror 111b, passes through a relay lens 116a, and reflects off a reflection mirror 114b. The blue light then passes through a relay lens 115b, further reflects off a reflection mirror 114c, and passes through the condenser lens 113B and the polarizing plate 112B. The blue light is then spatially modulated by the light valve 106B based on an image signal for a blue image and enters the prism 105. The rays of color light entering the prism 105 are composited by the prism 105 and enlarged and projected onto a screen and the like by the projection lens 116 through a mirror not shown.
Means are provided in the projector 100 for reducing heat of the optical components such as the light valves 106R, 106G and 106B and the polarizing plates 112R, 112G and 112B caused by heat of the light source 102 and heat produced by light emitted from the light source 102.
That is, as shown in FIG. 3, the related-art liquid crystal projector 100 includes a cooling fan 110 at the bottom of the optical unit 103 in the neighborhood of the light valve 106 (representing the light valves 106R, 106G and 106B) and the polarizing plate 112 (representing the polarizing plates 112R, 112G and 112B). Numeral 130 in FIG. 3 indicates light incident from the light source 102 on the optical unit 103.
As shown in FIG. 1, the projector 100 includes a duct unit 118 for supplying air currents to the cooling fan 110 by sucking outside air from an opening provided in the enclosure not shown. The duct unit 118 is made up of a duct not shown that is placed on the underside of the board 101 and connected to the cooling fan 110 and a duct 118b placed on the top surface of the board 101 and communicating with the other duct.
As shown in FIG. 4, intakes 123R, 123G and 123B are provided in the bottom of the optical unit 103 so that air currents supplied from the cooling fan 110 reach the light valves 106R, 106G and 106B and the polarizing plates 112R, 112G and 112B, respectively. Between the cooling fan 110 and the intakes 123R, 123G and 123B, a rib 117 in the shape of a nearly rectangular wall is provided for entirely surrounding the intakes 123R, 123G and 123B. In the region surrounded by the rib 117, dividers 122a and 122b are provided for separating the intakes 123R, 123G and 123B from one another. The rib 117 and the dividers 122a and 122b adjust a volume of air supplied to the light valves 106R, 106G and 106B. For example, the light valve 106B for spatially modulating short-wavelength blue light has a high light energy absorption factor and tends to be heated to a high temperature. In order to supply more air to the intake 123B, the positions of the rib 117 and the dividers 122a and 122b are appropriately adjusted so that the divided area corresponding to the intake 123B is larger than the other areas.
As shown in FIG. 1, a fine-mesh filter 119 is provided on the mouth of the duct 118b for preventing dust, bugs and so on from entering the apparatus from outside. As shown in FIG. 3, shield glasses 120a and 120b are fixed to the sides of the light valve 106 with an adhesive. A reduction in quality of a projected image due to dust and so on deposited on the light valve 106 is thereby prevented.
In the projector 100, the cooling fan 110 sucks outside air from the opening made in the enclosure, not shown, through the duct unit 118. The current of the sucked outside air is then supplied to the optical components such as the light valve 106 and the polarizing plate 112. The light valve 106, the polarizing plate 112, the condenser lens 113 (representing the condenser lenses 113R, 113G and 113B) and the prism 105 are thus cooled by the air supplied through the intake 123. The air heated in the optical unit 103 is exhausted from the part of the top of the optical unit 103 uncovered with the rid 121.
However, the following disadvantages are found in the related art projector 100 described so far, due to inefficiency of use of the air current supplied from the cooling fan 110.
(1) In order to increase the brightness of the image projected from the light valve 106, the quantity of light incident on the light valve 106 may be increased by raising the power of the light source 102 or improving the optical system (For example, the efficiency of use of light may be increased through the use of a polarization transforming device for transforming S polarized light [linearly polarized light whose electric field oscillates in the direction orthogonal to the incident surface] into P polarized light [linearly polarized light whose electric field oscillates in the direction parallel to the incident surface].). In this case, the optical components such as the light valve 106 and the polarizing plate 112 are heated to a high temperature and the properties thereof are degraded. To be specific, the light valve 106 may cause a change of colors when heated to 70.degree. C. or above, for example. The polarizing plate 112 may lose its polarizing function and not operate properly when hated to 80.degree. C. or above, for example. Such property degradation often results since the light valve 106B that transmits blue light has a high light energy absorption factor and tends to be heated to a high temperature, as described above.
(2) The life of the optical components such as the light valve 106 and the polarizing plate 112 is reduced when used under a high temperature.
(3) If a cooling fan that supplies a large volume of air at high air velocity is used in order to enhance the cooling efficiency, the noise increases and the product value of the projector is reduced.
(4) If the cooling fan is enlarged or the number of the cooling fan is increased for improving the cooling efficiency, the cost is increased as well as the size of the optical unit is increased.
Those disadvantages result in damage to the optical components including the light valve 106 and replacement thereof Convenience of the user is thereby affected and the cost of the projector is increased.